The present invention relates in general to motor vehicle suspension systems which include variable damping shock absorbers and preferably controllable springs, for example air springs, and, more particularly, to a method for controlling the shock absorbers in response to suspension frequency signals.
Motor vehicle suspension systems are connected between the body of the vehicle and the wheels to determine the ride and handling of the vehicle. Conventional suspension systems include springs and shock absorbers which are fixed such that the ride and handling are fixed as well.
More advanced suspension systems include controllable elements such as variable damping shock absorbers which permit two or more damping factors to be selected as needed. Controllable springs may also be included. Such springs are typically pneumatically or air controlled and are inflated to increase the spring rate of the overall vehicle spring system and deflated to decrease the spring rate.
In prior art suspension systems, the shocks and springs may be manually controlled by the operator of the vehicle. Automatic control is also utilized to control the shocks and springs in response to inputs from the vehicle as well. For example, the damping factor of the shock absorbers may be switched to a firmer damping in response to operating characteristics of the shock absorbers exceeding defined levels.
It is known to monitor shock absorber activity by means of accelerometers associated with the shock absorbers. The switching of the damping factor of the shock absorbers and the time of switching are then based on output signals from the accelerometers.
Such damping factor switching operations can be performed to substantially prevent body movements which can otherwise be caused by the switching. Prevention of the body movements is important to prevent operator concern regarding the ride and handling performance of the vehicle. Unfortunately, the inclusion of accelerometers in the suspension system results in complexity and expense.
Accordingly, there is a need for an improved suspension control system which can be simply and inexpensively implemented without accelerometers to control switching of the damping factor of variable damping shock absorbers such that the switches are substantially imperceptible to the operator of a motor vehicle.